Two closely related areas of research are proposed which will study control of arterial pressure in normo- and hypertensive animal models. The first area (Area I) will study both the short- and long-term consequences of intermittent stimulation of pressor areas in the central nervous system of free-running dogs. Data are acquired by telemetry techniques and stored directly into a digital computer for analysis. Factors are sought which potentiate the vascular response to threshold levels of intermittent stimulation. When these factors have been identified, they will be combined individually with long-term (weeks to months) central stimulation to test the hypothesis that CNS mechanisms are capable of initiating sustained hypertension only when other predisposing factors are present. The second are (Area II) proposed is for study of mechanisms underlying periodic oscillations in heart rate and mean blood pressure in telemetered dogs that are confined to a closed, isolated environment. Our preliminary studies have shown that oscillations of approximately 20-30 mmHg, peak-to-peak, occur in mean arterial pressures at frequencies of about 80-120 minutes. Furthermore, they occur throughout both light and dark cycles over a twenty-four hour period. Our studies will examine both central and peripheral mechanisms underlying these fluctuations in both normo- and hypertensive animals. Fast Fourier Transforms (FFT) are performed and frequencies and power densities are used as an index of the state of the cardiovascular controller. The over-all goal is to gain a clearer understanding of cardiovascular control systems and their dysfunction during the onset and established phases in experimental hypertensive models.